In wireless communication networks, recent developments of the 3GPP Long Term Evolution, LTE, facilitate accessing local IP based services in the home, the office, in public hot spot or even in outdoor environments. One area in which the access and local connectivity of these local IP based services may be used is in the direct communication between wireless devices in the close proximity of each other. In this case, close proximity may typically refer to less than a few tens of meters, but sometimes even up to a few hundred meters.
This direct mode or device-to-device, D2D, communication may demonstrate a number of potential gains over traditional cellular communication. This is because D2D devices are much closer to one another than other cellular devices that have to communicate via a cellular access point, e.g. a radio network node such as an eNodeB.
One of these potential gains is capacity. Radio resources, such as, e.g. Orthogonal Frequency-Division Multiplexing, OFDM, resource blocks, between the D2D and cellular layers may be reused, resulting in reuse gains. Also, the D2D link uses a single hop between the transmitter and receiver points as opposed to the double-hop link via a cellular access point, resulting in hop gains.
Another potential gain is peak rate. Because of the proximity, and potentially favorable propagation conditions for the D2D link, high peak rates are possible to achieve, resulting in proximity gains.
A further potential gain is latency. When wireless devices communicate over a direct D2D link, forwarding via the cellular access point is short-cut and the end-to-end latency between the wireless devices is decreased.
In these mixed cellular and D2D wireless communication networks, it has been suggested to locate D2D communication on cellular uplink, UL, resources in a way such that Time-Division Duplex, TDD, is the duplex transmission scheme of the D2D communication. This means that the cellular UL resources would be allocated for D2D communication transmission in both upstream and downstream directions between each D2D pair of wireless devices in a Time-Division Multiplexed, TDM, manner.
According to the current LTE protocol for cellular UL resources, there are two kinds of Uplink Control Information, UCI, which wireless devices transmit to the radio network node: a HARQ ACK/NACK for a cellular downlink, DL, PDSCH transmission, and a Channel State Indicator, CSI. PDSCH is short for Physical Downlink Shared CHannel. Also, the CSI which also may be referred to a channel-state report comprises a Channel Quality Indicator, CQI, a Precoding Matrix Indicator, PMI, and a Rank Indicator, RI.
The UCI may be carried on PUCCH or PUSCH to the radio network node. PUCCH is short for Physical Uplink Control CHannel, and PUSCH is short for Physical Uplink Shared CHannel. If there is PUSCH transmission in a current subframe, then the UCI may be multiplexed with data on PUSCH. If not, the UCI is transmitted on PUCCH.
However, in D2D communication, link adaptation is controlled autonomously by the D2D devices in the D2D pair instead of centrally by the cellular access point as for the cellular communication case. Thus, an efficient control signalling of the UCI in a D2D communication is desired.
Furthermore, data transmissions on the shared channels, PDSCH and PUSCH, are scheduled via the control channel, i.e. PDCCH. In the control signalling on the PDCCH, Transmission Format Command, TFC, information is included. The TFC information comprises the Modulation and Coding Scheme, MCS, format information of the data information that is scheduled for transmission on the PDSCH/PUSCH. The TFC information may further comprise e.g. HARQ information, a New Data Indicator—NDI, and/or Redundancy Version, RV, information.
Here, the MCS format information indicates which MCS format is applied to the data information. The MCS format information is determined locally at the D2D devices for the D2D communication. Hence, an efficient control signalling of the TFC information in a D2D communication is desired.